Fastening system for internal fixation

ABSTRACT

A bone fracture fixation system comprises a bone plate configured to bear against a proximal surface of the bone and a plurality of elongated tension elements, each sized to pass through an opening in the bone plate and through the bone from the proximal surface to a distal surface thereof. Each tension element is anchored to the bone and maintained in tension by a distal anchor attached to said tension element and configured to engage the distal surface of the bone and a proximal anchor engageable between the bone plate and the tension element. In one method for fixation of a bone fracture, the bone plate is positioned on a proximal surface of the bone while the tension element is introduced into the bone and through an opening in the bone plate from an opposite distal surface of the bone.

BACKGROUND OF THE INVENTION

The present invention relates to a system for internal fixation of abone, and especially for the fixation of fractures of the bone.

For any bone fracture, the orthopaedic specialist must first reduce thefracture and then adequately stabilize and fix the bone to maintain thereduction as the bone heals. Each of these steps is complicated when thebone has suffered multiple fractures or a fracture that is not simplytransverse. Fractures of this type usually require some form of internalfixation to reduce and maintain the bone fragments. One conventionalapproach to reducing bone fragments is with a bone plate extending overa portion of the bone at the fracture site. In one surgical approach, anorthopaedic surgeon may use a specialized clamp applied across the bonewhile attaching the fixation plate to the bone by screwing a pluralityof screw fasteners through holes in the plate into the underlying bone.

Generally, screw fasteners are effective in holding the bone platetightly against the healthy bone so that fracture may heal properly.However, in less healthy (e.g., osteopenic) bone, the screw threads maynot find adequate purchase in the bone to hold the bone and platetogether in proper alignment. This may result in non-union of thefracture that may require more invasive revision surgery to correct.

Another problem associated with screw fasteners is occasional breakageof the screw near the plate-bone interface due to stress concentrationsarising from poor load sharing among all of the screws and/or highcyclic loading.

A further drawback of the screw fastener approach to internal fixationis that a large variety of screw sizes must be made available for eachsurgical procedure in order to accommodate variations in patient anatomyand fracture type. Maintaining a large inventory of screw sizes, alongwith the appropriately sized drills, guides, drivers and fixtures, canbe costly. There is also the chance that an inappropriately sized screwmay be selected during a procedure.

Fixation approaches have been developed that do not rely upon screwfasteners. For example, cerclage systems utilize one or more cablestightened around a bone to hold the fracture fragments together. Thecable construct may include a plate that helps anchor the cables.However, cerclage systems require access around the entire periphery ofthe bone so it is necessary for the surgeon to dissect soft tissuessurrounding the bone. Another problem is that the cerclage cable canexert significant line pressure against the periosteum, which may injurethe bone and inhibit healing.

Accordingly, there is a need for a fracture fixation system thatprovides a stable construct in osteopenic bone and that may be adaptedfor minimally invasive surgical procedures. There is also a need for afracture fixation system that reduces the inventory of fasteners andassociated instrumentation required during the surgical procedure. Thereis a further need for a fracture fixation system that assists inimproving and maintaining the fracture reduction during application andthat incorporates fasteners that resist breakage after implantation andthat are less technique sensitive to apply than conventional bonescrews.

SUMMARY OF THE INVENTION

In order to address these needs, the present invention provides afracture fixation system that comprises a bone plate configured to bearagainst a proximal surface of the bone, the bone plate defining aplurality of openings therethrough. A plurality of elongated tensionelements are provided, each sized to pass through one of the bone plateopenings and through the bone from the proximal surface to a distalsurface thereof. A distal anchor is attached to each tension element andconfigured to engage the distal surface of the bone when the tensionelement passes through the bone. A proximal anchor is engageable betweenthe bone plate and each tension element to maintain tension in thetension element between the proximal anchor and the distal anchor. Thetension element may be a braided metal cable or similar elongatedelement.

In one embodiment, the proximal anchor is a Tinnerman washer. In thisembodiment, the bone plate defines a recess around at least some of theplurality of openings. The Tinnerman washer is sized to be receivedwithin the recess and is configured to engage the tension elementpassing therethrough to maintain tension on the element.

In other embodiments, the proximal anchor is configured for a polyaxialinterface with the bone plate. With this feature, the tension elementmay be situated at a range of angles relative to the bone plate tooptimize the ability of the surgeon to reduce multiple bone fracturefragments. In these embodiments, at least some of the openings define aspherical wall and include a locking bushing disposed therein. Thelocking bushing has a spherical outer surface for complementaryengagement with the spherical wall, and further includes an internallythreaded bore. The proximal anchor includes a central bore for receivingthe tension element therethrough and a threaded head. The head of theanchor and the locking bushing define a tapered threaded interface sothat the bushing expands into the spherical wall as the head is threadedinto the bushing.

In one aspect, the distal anchor has a shape memory component with afirst configuration sized to pass through the bone plate openings andthrough the bone from the proximal surface to a distal surface thereof.The shape memory component has a second shape memory configuration forengaging the distal surface of the bone. In one embodiment, the distalanchor includes at least two prongs that are substantially aligned withthe elongated tension element in the first configuration and extendedoutward therefrom in the second shape memory configuration. The prongsmay be spring elements or may be formed of a shape memory metal.

In other embodiments, the distal anchor is a fixed shape component thatis sized to bear against the distal surface of the bone. Thus, thedistal anchor may be a disc or a generally spherical element. Inspecific embodiments, the distal anchor may also include a washer with arecess to receive the spherical element therein.

The present invention contemplates a method for fixation of a bonefracture that comprises positioning a bone plate on a proximal surfaceof the bone, the bone plate including a plurality of openingstherethrough and passing at least two elongated tension elements throughplate openings and through the bone to a distal surface thereof. Eachtension elements is anchored to the distal surface of the bone and thenplaced in tension. The proximal end of the tension element is thenanchored to the bone plate while maintaining the tension in the element.To facilitate passage of each tension element through the bone, a K-wireor stylet may be used to form an appropriately oriented path and asheath may be used to help convey the tension element, and in some casesthe distal anchor, through the bone.

In accordance with one embodiment of the invention, a tool is providedfor use with a pair of elongated medical devices. The tool comprises abarrel defining an elongated bore open between a proximal end and adistal end that is sized to receive an elongated medical device at acorresponding one of the proximal and distal ends. The barrel furtherdefines a first side opening communicating with the elongated boreextending from the proximal end toward the distal end, and a second sideopening also communicating with the elongated bore but extending fromthe distal end toward the proximal end. The second side opening isangularly offset relative to the first side opening and is connected tothe first side opening by an intermediate side opening defined in thebarrel. The side openings are sized to permit removal of one of theelongated medical devices from the elongated bore.

The tool is used by introducing an end of one of the elongated medicaldevices into the proximal end of the barrel and an end of the otherelongated medical device into the distal end of the barrel. The two endsof the elongated devices mate within the barrel so that the barrel canserve as a guide for advancement of the elongated medical devicestherethrough. The tool can thus be used for positioning an elongatedmedical element within a bone.

In a further aspect of the invention a method for positioning theelongated medical device within a bone comprises extending a firstelongated element through a bone so that a distal end of the firstelement extends outside the bone and then mating a proximal end of asecond elongated element with the distal end of the first element. Thetool may be used to perform this mating step.

In a further aspect of the method, the second elongated element ispushed into the bone while maintaining the proximal end and the distalend in mating contact. Once the proximal end of the second element hasexited the bone, the first element may be removed. In certainembodiments of the invention, the second elongated element is a tensionelement used to reduce and fix a bone fracture.

In one aspect, elongated elements includes a recess and the other of theelements includes a tip adapted to be received within the recess. In aspecific embodiment, the first element is a K-wire having a sharpenedtip at its distal end, while the second element is a tension cablehaving a recess at its proximal end.

In a further embodiment of the invention, a method is provided forfixation of a bone fracture. This method comprises the steps of:

(a) providing a bone plate including a plurality of openings andpositioning the bone plate on the surface of the bone;

(b) extending a first elongated element through the bone so that adistal end of the first element extends outside the bone;

(c) providing an elongated tension element having an anchor portion at adistal end thereof;

(d) mating a proximal end of the tension element with the distal end ofthe first element;

(e) pushing the tension element into the bone while maintaining theproximal end and the distal end in mating contact until the anchorportion of the tension element contacts the bone;

(f) removing the first element from the tension element when theproximal end of the second element exits the bone;

(g) extending the proximal end of the tension element through one of theopenings in the bone plate;

(h) tensioning the tension element; and

(i) while maintaining the tension element in tension, anchoring thetension element to the bone plate.

In certain embodiments, the first elongated element is a K-wire having asharpened tip, wherein the K-wire is driven through the bone by a drill.In the preferred embodiment, the bone plate is positioned on the boneprior to extending the first elongated element through the one of theopenings in the plate. The bone plate may thus serve as a guide fororienting and positioning a second tension element within the bone.

In one aspect of the inventive method, he step of anchoring the tensionelement to the bone plate includes extending a cannulated drill over theproximal end of the tension element and forming a bore at leastpartially into the bone using the cannulated drill. A cannulated anchorelement is advanced along the proximal end of the tension element,through an opening in the bone plate and into the bore formed in thebone.

The present invention contemplates that the method steps are repeatedfor a plurality of tension elements to effectively reduce bone fragmentsof the fracture. The step of anchoring all the tension elements to thebone plate may include adjusting the tension in selected ones of thetension elements prior to anchoring the selected tension elements. Onceall of the tension elements have been properly tensioned and anchored tothe bone plate, the excess portions of the elements are severed andremoved.

One significant benefit of the fracture fixation system of the presentinvention is that it is well suited for use in soft, osteopenic bonethat is otherwise incapable of supporting a lag screw. At the same time,the tension elements provide a lag effect for optimal fracturereduction.

Another benefit is that the tension elements and anchors may be providedas “one size fits all”. In other words, once the tension elements aretensioned and anchored, any excess material is removed. The necessarysize of the tension element need not be determined prior toimplantation. The tension element may be arranged to pass directlyacross the bone or across long spans of the bone without requiringdifferently sized elements.

It is one important object of the invention to provide a fracturefixation system that is particularly well suited for use in reducingmultiple fracture fragments. It is another object to provide a fixationsystem that can be used equally well with healthy or less than healthybone. Other objects and benefits of the invention will become apparentupon consideration of the following written description along with theaccompanying figures.

One significant benefit of the fracture fixation system of the presentinvention is that it is well suited for use in soft, osteopenic bonethat is otherwise incapable of supporting a lag screw. At the same time,the tension elements provide a lag effect for optimal fracturereduction.

Another benefit is that the tension elements and anchors may be providedas “one size fits all”. In other words, once the tension elements aretensioned and anchored, any excess material is removed. The necessarysize of the tension element need not be determined prior toimplantation. The tension element may be arranged to pass directlyacross the bone or across long spans of the bone without requiringdifferently sized elements.

It is one important object of the invention to provide a fracturefixation system that is particularly well suited for use in reducingmultiple fracture fragments. It is another object to provide a fixationsystem that can be used equally well with healthy or less than healthybone. Other objects and benefits of the invention will become apparentupon consideration of the following written description along with theaccompanying figures.

DESCRIPTION OF THE FIGURES

FIG. 1 is a side perspective of a fracture fixation system according toone embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of the fracture fixationsystem shown in FIG. 1.

FIG. 3 is an enlarged cross-sectional view of a fracture fixation systemaccording to a further embodiment of the invention.

FIG. 4 is an enlarged perspective view of a proximal anchor used in thefracture fixation system shown in FIG. 3.

FIG. 5 is an enlarged perspective partial view of the working end of adriving tool for driving the proximal anchor shown in FIG. 4.

FIGS. 6 a, 6 b are side views of a distal anchor for use with thefracture fixation system shown in FIG. 1 according to one embodiment ofthe invention, with the distal anchor shown in its non-extended andextended states.

FIGS. 7 a, 7 b are side partial cross-sectional views of the distalanchor depicted in FIGS. 6 a, 6 b, shown with the distal anchor within abone in its extended and tensioned states.

FIGS. 8 a, 8 b are side partial cross-sectional and bottom views of adistal anchor for use with the fracture fixation system shown in FIG. 1,according to a further embodiment of the invention.

FIG. 9 is a side perspective view of a distal anchor for use with thefracture fixation system shown in FIG. 1, according to still anotherembodiment of the invention.

FIGS. 10 a, 10 b are side views of additional distal anchors of a distalanchor for use with the fracture fixation system shown in FIG. 1.

FIG. 11 a is a side view of a tension element and distal anchor for usewith the fracture fixation system shown in FIG. 1, according to oneembodiment of the invention.

FIG. 11 b is an enlarged partial cross-sectional view of the proximalend of the tension element shown in FIG. 11 a.

FIG. 12 is a perspective view of an exchange tool for use in a surgicalprocedure to fix the fixation system shown in FIG. 1 to a bone.

FIGS. 13 a, 13 b are side and end views of the exchange tool shown inFIG. 12.

FIG. 14 is a representation of a first step in a method for fixing afixation system as shown in FIG. 1 to reduce and fix a fractured bone,in accordance with one embodiment of the invention.

FIG. 15 is a representation of a further step in the method for fixing afixation system to reduce and fix a fractured bone.

FIG. 16 is an enlarged partial cross-sectional view of the interfacebetween a tension element and a K-wire, designated as area A in FIG. 15.

FIGS. 17-20 are representations of subsequent steps in the method forfixing a fixation system as shown in FIG. 1 in accordance with oneembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the invention is therebyintended. It is further understood that the present invention includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles of the invention aswould normally occur to one skilled in the art to which this inventionpertains.

The present invention contemplates a system for reducing and fixing bonefractures, such as the fractures F in bone B shown in FIG. 1. Thepresent system is particularly suited for fractures with multiple bonefragments that require precise reduction and secure fixation to maintainthe reduction as the bone mends. In accordance with one embodiment, abone plate 10 is positioned on the bone in a conventional manner. Thebone plate may be of many known configurations that incorporate a seriesof recesses (FIG. 2). In one embodiment, bone screws 12 may be used toanchor one end of the bone plate 10 away from the fractures F. Thesescrews help anchor the fixation arrangement in viable bone and can alsohelp hold the plate as other fixation elements are introduced into thebone.

In accordance with the present invention, it is contemplated that afixation system 20 includes a plurality of tension elements 22 that areadapted to work with the plate 10 to reduce the fractures F in the boneB. The tension elements are configured to extend through the recess 14and opening 14 a in the bone plate 10 and through a bore 18 formed inthe bone, as shown in FIG. 2. The tension elements 22 are therefor sizedto span from a proximal surface P to an opposite distal surface D of thebone B. The distal end of the tension elements 22 is provided with adistal anchor 24 which may come in a variety of forms that are adaptedto anchor against the cortical bone C at the distal surface D of thebone when tension is applied to the tension element 22. A proximalanchor 26 engages the proximal end of the tension element to the boneplate at the proximal surface P of the bone and is configured to holdtension in the tension element 22.

The tension element 22 is an elongated flexible element that is capableof being pulled into tension and then anchored at its opposite ends. Incertain embodiments, the tension element may be a braided metal cable, amonofilament or braided suture, or a biocompatible wire. When thefixation system 20 is initially installed, the tension element 22includes an excess portion 28 that projects beyond the bone B and plate10. Once the proximal anchor 26 is fixed, the excess portion 28 can besevered, leaving a cut end 29 that is preferably as close to theproximal surface P of the bone B as possible. The tension element can besevered using a tool appropriate for the particular material of theelement.

In the embodiment illustrated in FIGS. 1-2, the proximal anchor 26 is agripping washer, such as a Tinnerman washer. As is known in the art, aTinnerman washer includes a conical central portion 26 a having acentral opening 26 b. In accordance with the present invention, thecentral opening 26 b has an effective diameter slightly less than theeffective diameter of the tension element 22. As depicted in FIG. 2, theproximal anchor or washer 26 is positioned within the recess 14 in theplate 10 with the conical portion 26 a projecting outward from theplate. With this orientation, the proximal anchor 26 can hold thetension in the element 22 since any pull opposite the tension directionT will tend to dig the element into the opening 26 b and will try tocompress the conical portion 26 a. The walls of the recess 14 keep thewasher 26 from flattening so that the washer will act to maintain thetension in the element 22 between distal and proximal anchors 24, 26.

An alternative proximal anchor 30 is illustrated in FIGS. 3-4. Thisanchor is especially adapted for use with a bone plate 10′ that issimilar to the polyaxial locking plate disclosed in U.S. Pat. No.5,954,722 (the '722 Patent), the disclosure of which is incorporatedherein by reference. This locking plate includes a plurality ofthru-holes 14′ in which the wall of the holes is generally spherical. Alocking bushing 16 similar to the bushing disclosed in the '722 Patentis configured to fit within the spherical walls of the thru-holes 14′ sothat the bushing can assume a range of angular orientations relative tothe plate 10′. The bushing 16 is provided with internal threads 17. Asdisclosed in the '722 Patent, the locking bushing is configured toreceive the tapered threaded head of a bone screw so that as the head isthreaded into the internal threads 17 the bushing 16 expands outwardlyinto the spherical surface of the thru-bore 14′ to lock the bushing, andhence the bone screw, at the particular angular orientation relative tothe locking plate.

The proximal anchor 30 of this embodiment includes a non-threaded shank32 that is configured to extend through the plate 10′ and into the bonebore 18 in the bone B. In one specific embodiment, the shank 32 may betapered to form a press-fit engagement within the cortical bone C nearthe proximal surface P of the bone B. The proximal anchor 30 furtherincludes a tapered head 34 that carries external threads 36 for engagingthe internal threads 17 of the locking bushing 16. Like the bone screwin the '722 Patent, the tapered head 34 of the proximal anchor 30expands the bushing as the head is threaded into the bushing, therebylocking the bushing within the spherical walls of the thru-hole 14′ inthe plate 10′. Thus, as with the bone screw in the '722 Patent, theproximal anchor 30 incorporates a polyaxial capability that allows theanchor to assume a range of angular orientations relative to the boneplate 10′. This polyaxial capability allows the tension element 22passing through the anchor 30 to assume a comparable range of anglesrelative to the plate when the element is tensioned and anchored. Thus,it can be seen that the polyaxial capability enhances a surgeon'sability to reduce difficult bone fragments and hold that reduction overtime.

As seen in FIG. 4, the proximal anchor 30 defines a central bore 40through which the tension element 22 extends, as depicted in FIG. 22. Inorder to provide a clamping effect on the tension element, the anchor 30further defines an array of cross-slots 38 passing through the centralbore 40. As the head portion 34 is threaded into the locking bushing 16,the cross-slots 38 allow the effective diameter of the central bore 40to decrease, thereby compressing about the tension element. As with theTinnerman washer 26 discussed above, any pulling force on the tensionelement 22 will tend to pull the head 34 of the proximal anchor 30deeper into the bushing 16, which has the effect of further closing thecross-slots and central bore around the tension element. Thus, the headportion 34 of the proximal anchor accomplishes two lockingfunctions—first, locking the angular orientation of the anchor relativeto the plate, and second, locking the tension element within the anchor.

In one specific embodiment, the head portion 34 defines driving lugs 42on the proximal face thereof. A driving tool, such as the tool 50 shownin FIG. 5, may engage the lugs to permit rotation of the proximalanchor. The driving tool 50 is cannulated 52 with drive slots 54configured to tightly engage the lugs 42 on the proximal anchor. Thecannulated aspect of the tool 50 allows the tool to be used to drive theproximal anchor into the bone plate 10′ while the excess portion 28 ofthe tension element is still available for tensioning the element.

In a method of using the fixation system 20 of the present invention, abone plate 10, 10′ is positioned on the bone B so that the plateopenings 14 a, 14′ are optimally oriented for reducing the bonefragments of the fracture F. One end of the bone plate may be anchoredto the bone B using fasteners, such as the screws 12 shown in FIG. 1. Adrill guide is then mounted over a plate opening and an orthopaedicdrill is used to form the bone bore 18 through the bone B, exiting atthe distal surface D. A K-wire may be first inserted to help guide thebone drill. The bone bore 18 is preferably sized slightly larger thanthe effective diameter of the tension element 22. In the embodiment ofthe fixation system that uses the proximal anchors 30, a larger diameterbone bore 18 may be formed in the proximal cortical bone C forengagement by the shank 32 of the anchor, as depicted in FIG. 3.

Once the bone bore 18 has been formed, a tension element 22 is passedthrough the plate opening and bone bore until the distal anchor 24 hasexited at the distal surface D of the bone. In certain embodiments, anintroducer sheath (not shown) may be first positioned within the bonebore 18 to facilitate passage of the tension element. With the distalanchor 24 in position, the proximal anchor 26 or 30 is threaded onto theproximal end of the tension element. Tension may be applied to thetension element by pulling at the excess portion 28 of the element 22. Acable tensioning device, such as the device disclosed in U.S. Pat. No.6,595,994 (the '994 Patent), the disclosure of which is incorporatedherein by reference, may be adapted to engage the tension element 22 andapply tension to the element in a manner that permits fixation of theelement by the proximal anchor. In one approach, the working end of thedevice disclose din the '994 Patent can bear against the proximal anchorTinnerman washer 26 as the tension element or cable is pulled in thetension direction T (FIG. 2). In a further embodiment, the working endof the cable tensioning device in the '994 Patent may be modified tobear against the proximal face of the anchor 30 (FIG. 4). Moreover, theworking end of the tensioning device may be modified to incorporate thedriving tool 50 (FIG. 5). In this further embodiment, once theappropriate tension has been applied to the element 22, the proximalanchor 30 may be tightened into the locking washer 16 to fix theconstruct.

The distal anchor 24 is configured to engage the distal surface D of thebone B when tension is applied and maintained in the tension element 22.In one specific embodiment, the distal anchor may include wings 25 (FIG.2) that pivot outward once the distal end has exited the bone bore 18 atthe distal surface D. The wings may be propelled outward by a torsionspring disposed within the distal tip of the tension element.

In an alternative embodiment illustrated in FIGS. 6 a-7 b, the distalanchor incorporates shape memory technology. In this embodiment, atension element 60 includes prongs 64 that exhibit shape memory to moveto an expanded orientation 64′ shown in FIG. 6 b. This shape memoryfeature may be provided by pre-bending the distal end of the tensionelement 60 so that the prongs spring outward to the position shown inFIG. 6 b. In order to introduce the tension element through the plate10/10′ and the bone bore 18, the element 60 is threaded into anintroducer sheath 62 with the prongs maintained within the sheath as thesheath and tension element are passed through the bone plate and bonebore. Once the prongs 64 are positioned at the distal surface D of thebone, the sheath may be retracted, allowing the prongs to assume theiranchoring configuration. One benefit of this shape memory feature isthat the tension element may be removed by dislodging the distal anchor,which can advantageously be accomplished by extending the sheath 62 backalong the tension element until it contacts the prongs and draw theminward within the sheath.

The tension element 60, and more particularly the shape memory prongs64, may be configured to enhance their anchoring capability when thetension element 60 is tensioned. In particular, as illustrated in FIG. 7a, the tension element 60 may be positioned initially with the body 66extending through the plate and bone and with the prongs 64 in aninitial extended orientation. This initial orientation nominallycorresponds to the free state of the shape memory prongs when leftunconstrained. As tension is applied to the body 66, the prongs flattenfrom their initial orientation by a distance S. In this tensionedconfiguration the prongs 64 act as springs to increase the tension T2 inthe body 66 from the original tension T1 (FIG. 7 a). This characteristicof the tension element 60 may be used to control the amount of tensionapplied to the element and prevent over-tensioning. For instance, the“flatness” of the prongs may be gauged to provide an indication of thetension. It may also be contemplated that under excess tension theprongs 64 will invert and begin to move into the bone bore, which thushas the effect of dumping the tension in the element 60.

In one specific embodiment, the prongs 64 are formed of a springmaterial, such as medical grade spring steel. In another embodiment, theprongs are formed of a shape memory metal, such as NITINOL ™ As is knownin the art, a shape memory metal changes shape at a pre-determinedtemperature, which is typically near body temperature.

In the embodiment depicted in FIGS. 6 a-6 b, the tension element 60includes a pair of opposite prongs 64. In another specific embodiment, atension element 70 may include more than two prongs 72 extending from anelongated body 74. The multiple prongs 72 preferably exhibit the sameshape memory characteristics as the prongs 64 described above. In yetanother embodiment, a tension element 80 includes an elongated body 86terminating in a distal portion 84. A curl element 82 separates from thedistal portion 84 when the distal end is adjacent the distal surface Dof the bone B. The curl element 82 may have a normal, unloaded radius ofcurvature, while the radius is reduced when tension is applied to thebody 86. As the radius decreases, the curl element 82 exerts a greaterresistance, thereby increasing the tension, as with the tension element60 described above.

In other embodiments of the invention, the distal anchor may incorporatea fixed component. For instance, as shown in FIG. 10 a, the tensionelement 22 terminates in a disc 24. In an alternative embodiment, thetension element 22 may terminate in a rounded element 24′. The roundedelement 24′ has one radius of curvature R1 and a larger radius ofcurvature R2 at the surface that contacts the soft tissue surroundingthe bone in order to minimize the trauma to the adjacent tissue. Thesmaller radius R1 is configured to sit within a complementary configuredrecess 27 a of a washer 27 that is disposed between the bone and thedistal anchor. This washer/anchor interface permits variable angularorientations while ensuring uniform load distribution on the distalsurface of the bone. In yet another specific embodiment, the distalanchor may constitute a spherical ball 92 fixed at the end of the body94 of a tension element 90, as illustrated in FIG. 11 a.

One common attribute of the embodiments shown in FIGS. 10 a, 10 b and 11a is that the distal anchors are, in effect, rigid, and incapable ofpassing through the plate opening 14/14′ or the bone opening 18. Thus,unlike the shape memory anchors of FIGS. 6 a-9, the tension elementswith the distal anchors 24, 24′ and 92 cannot be inserted from theproximal surface P of the bone B. A further embodiment of the inventioncontemplates a system and method for introducing these tension elementsthrough the distal surface D to mate with a bone plate at the proximalsurface P, all in a minimally invasive procedure.

In this embodiment, an exchange tool 100 that is used to facilitateretrograde movement of the proximal end 96 of the tension element 90through a bone bore. As shown in FIGS. 12, 13 a and 13 b, the tool 100includes a barrel 102 that defines a bore 104 therethrough that is sizedto receive the elongated body 94 of the tension element 90. The barrel102 defines a side opening 106 at a proximal portion of the barrel and adistal side opening 108 at a distal portion. The distal side opening 108is offset from the proximal side opening 106 although the two sideopenings are contiguous through a connecting slot 110. The tool 100further includes a handle 112 connected to the barrel 102 that is usedto manipulate the exchange tool as described below. As best seen in FIG.13 b, the two side openings 106 and 108 are preferably about 180° apart.

The exchange tool is used in the series of steps depicted in FIGS.14-19. In a first step, a bone plate 10′ is shaped to fit a bone Badjacent a fracture site F. As described above, the bone plate 10′ maybe anchored by bone screws 12 positioned apart from the fracture site. Aguide 150 is positioned within a plate opening 14′ that is aligned witha desired fixation location. It can be appreciated that a pattern offixation may be pre-planned based on radiographic images of the bonefragments. As shown in FIG. 14, a first tension element may beintroduced to span numerous fractures at the head of the bone B. Theguide 150 is sized to receive a K-wire 152. The K-wire is operativelycoupled to a drill 154 that is used to drive the K-wire through the boneat a desired angle relative to the plate 10′. In the above-describedembodiments that utilize the shape memory feature, it is necessary toform the bone bore 18 so that the distal anchor may be conveyed throughthe bone. In the embodiment of FIGS. 14-19, it is not necessary toinitially form the bone bore since the distal anchor will be introducedfrom the distal surface D of the bone.

The K-wire 152 has a sharpened tip 153 adapted to penetrate bone. Othersimilar devices may be used, such as a thin gage stylet. In analternative approach, a separate drill bit may be used to form a narrowbore through the bone, with the K-wire, stylet or similar elongatedelement advanced through the bore. In this alternative approach, thedrilled bore preferably has a diameter smaller than the diameter of theK-wire or stylet.

Once the K-wire has exited the bone through the distal surface, theexchange tool 100 is positioned over the distal tip of the K-wire 152 sothat the K-wire extends through the central bore 102, as shown in thedetail view of FIG. 16. The proximal end 96 of the tension element 90 isthen introduced into the bore 102 from the distal end of the tool 100.As shown in FIG. 11 b, the proximal end 96 defines a conical recess 98.This recess is configured to accept the tapered tip 153 of the K-wire,as depicted in FIG. 16. It can thus be appreciated that the exchangetool 100 provides a mechanism for aligning the elongated body 94 of thetension element 90 with the K-wire 152 at the distal side of the bone B.

With the K-wire and tension element united within the exchange tool, thebarrel 102 of the tool is preferably moved into contact with or at leastimmediately adjacent the distal surface D of the bone. The body 94 ofthe tension element 90 is then pushed retrograde toward the bone B, asshown in FIG. 15. As the tension element moves toward the bone, theproximal end 96 pushes the K-wire 152 out of the bone. It can beappreciated that once the K-wire/tension element interface reaches thebone B, the exchange tool 100 is no longer required to maintain thatinterface. Thus, the tool may be readily removed by rotating the tool inthe direction of the arrow in FIG. 17 so that the tool essentiallypivots about the connecting slot 110. As the tool is pivoted, theelongated body 94 of the tension element automatically exits the centralbore 104 through the side slots 106, 108, leaving only a portion of thebody 94 within the connecting slot 110. The exchange tool 100 is thencompletely removed by sliding the connecting slot 110 off the tensionelement.

With the exchange tool removed, the bore formed in the bone by theintroduction of the K-wire serves to guide the tension element 90 towardthe proximal surface P of the bone. Eventually the tip 153 of the K-wireexits the bone at the proximal surface P and the K-wire can be removed.The tension element is then advanced farther through the bone until thedistal anchor 92 contacts the distal surface D of the bone.

It can be appreciated that the exchange tool initially and the bore inthe bone subsequently help maintain the tension element 90 in alignment.The central bore 104 in the exchange tool and the bone bore are onlyslightly greater in diameter than the body 94 of the tension element sothe body cannot flex or buckle as the tension element is movedretrograde into and through the bone. Thus, even if the tension elementexhibits lateral flexibility, it can still be advanced into the bone inthe manner described.

At this point, the tension element 90 is available to receive a proximalanchor to reduce the fracture and fix the tension element to the boneplate. In the case of the anchor 26 shown in FIGS. 1-2, the Tinnermanwasher may be threaded onto the exposed portion of the tension elementand tightened as described above. For the anchor 30 shown in FIGS. 3-4,the next step of the process includes advancing a cannulated drill 160over the tension element, as depicted in FIG. 18. The cannulated drillmay form the bone bore 18 to a depth sufficient to accept the shank 32of the proximal anchor 30. This depth will vary depending upon thelength of the shank 32. In some cases, the shank will extend across thebone to the cortical bone at the distal surface, while in the typicalcase the shank will only project partially into the bone. With tensionmaintained on the body 94 of the tension element, the proximal anchor 30is driven into the bone using tool 50 and into locking bushing 16 of theplate 10′, as illustrated in FIG. 19. This process can be repeated at anumber of locations on the bone plate 10′, as shown in FIG. 20. Thetension at each tension element may be adjusted throughout the process,even as other tension elements are being added to the construct, to evenout the plate compression on the bone or other wise adjust the positionof the plate. Once the surgeon is satisfied with the tension andorientation of all of the tension elements, the excess tension elementmaterial may be removed.

The tension element 22 is preferably a braided metal cable or similarmedical grade material suitable for implantation in a patient. In thepreferred embodiment, the tension element does not elongatesignificantly under tension. It is expected that the tensioning processmay be iterative as the tension element stretches slightly as load isapplied. A gauge may be used to verify the cable tension. In alternativeembodiments, the tension element is formed of a more elastic material,such as a silicone rubber cord, or may incorporate a spring element witha calibrated stiffness.

In the illustrated embodiments, a single tension element is provided ateach hole location in the bone plate 10/10′. Alternatively, multipletension elements may be anchored at a common plate recess 14 or opening14′. Each tension elements may be deployed at different angles relativeto the bone plate.

The tension elements and distal anchors may be provided in a range ofsizes depending upon the type of fracture being treated. For instance,the tension element may have an effective diameter of about 1-3 mm alength of 100-200 mm. The distal anchors 24, 24′ and 92 may have aneffective diameter of about 4-6 mm.

The size of the proximal anchors are dictated in some degree by thedimensions of the bone plate to which these anchors are fixed. Forinstance, the diameter of the Tinnerman washer 26 or the threadedtapered head 34 of the anchor 30 are determined by the internal diameterof the recess 14 and locking bushing 16, respectively. The height of theproximal anchors are preferably set so that the anchors do not projectoutside the exposed surface of the bone plate, to minimize trauma tosurrounding tissue.

In the certain embodiments, the distal anchors may be integral with thetension element. In other embodiments, the distal anchors arepermanently attached to the tension element in a known manner, such asby crimping or welding. It is expected, however, that the attachmentbetween tension element and distal anchor be sufficiently strong towithstand the tension applied to the element.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe invention are desired to be protected.

For example, the proximal anchor 30 contemplates a tapered threadedengagement between the bone plate and the anchor, via the lockingbushing. Alternatively, the opening 14′ in the bone plate 10′ (FIG. 3)may be tapered, such as a Morse taper. The threads 36 may be eliminatedon the head 34 of the proximal anchor 30 (FIGS. 3-4) so that the head 34is a smooth tapered component, while retaining the cross-slots 38.Rather than threading the proximal anchor into the locking bushing, thetapered head may be pressed into the mating tapered opening in the boneplate while the tension element 22 is maintained in tension. With thisalternative embodiment, the driving lugs 42 may also be eliminated. Thedriving tool 50 may be replaced with a cannulated impact driver. Inorder to retain the polyaxial or variable angle capability, the lockingbushing may incorporate the complementary mating angle for press-fitengagement with the tapered head of the modified proximal anchor. Theplate opening 14′ may then retain its spherical inner surface to matewith the spherical outer surface of the bushing at a range of anglesrelative to the plate.

1. A tool for use with a pair of elongated medical devices comprising: abarrel defining an elongated bore open between a proximal end and adistal end and sized to receive an elongated medical device at acorresponding one of said proximal and distal ends; a first side openingdefined in said barrel and communicating with said elongated boreextending from said proximal end toward said distal end; a second sideopening defined in said barrel and communicating with said elongatedbore extending from said distal end toward said proximal end, saidsecond side opening angularly offset relative to said first sideopening; and an intermediate side opening defined in said barrel andcommunicating with said elongated bore, said intermediate side openingcommunicating between said first and second side openings, wherein saidside openings are sized to permit removal of one of said elongatedmedical devices from said elongated bore and wherein said barrelincludes an insertion portion that is sized and configured forpercutaneous insertion into the body of a patient.
 2. The tool of claim1, wherein said intermediate side opening is disposed closer to saiddistal end than to said proximal end.
 3. The tool of claim 1, furthercomprising a handle attached to said barrel and proximal to saidinsertion portion to permit manual manipulation of said barrel.
 4. Amethod for positioning an elongated medical element within a bonecomprising: extending a first elongated element through a bone so that adistal end of the first element extends outside the bone; mating aproximal end of a second elongated element with the distal end of thefirst element; pushing the second elongated element into the bone whilemaintaining the proximal end and the distal end in mating contact; andremoving the first element from the second element when the proximal endof the second element exits the bone.
 5. The method for positioning anelongated medical element of claim 4, wherein the one of the distal endand proximal end has a recess and the other of the distal end andproximal end has a tip adapted to be received within the recess, and themating step includes positioning the tip within the recess.
 6. Themethod for positioning an elongated medical element of claim 5, whereinthe first element is a stylet having a sharpened tip at its distal endand the second element includes the recess.
 7. The method forpositioning an elongated medical element of claim 6, wherein the secondelement is a wire.
 8. The method for positioning an elongated medicalelement of claim 4, wherein the mating step includes: providing anexchange tool having a bore sized to receive the first and secondelements therethrough; extending the distal end of the first elementinto the proximal end of the bore of the exchange tool; extending theproximal end of the second element into the distal end of the bore ofthe exchange tool until the proximal end of the second element mateswith the distal end of the first element.
 9. The method for positioningan elongated medical element of claim 8, wherein the exchange toolguides the second element as it is pushed into the bone.
 10. The methodfor positioning an elongated medical element of claim 9, wherein theexchange tool is removed when the second element is within the bone. 11.A method for fixation of a bone fracture comprising: (a) providing abone plate including a plurality of openings and positioning the boneplate on the surface of the bone; (b) extending a first elongatedelement through the bone so that a distal end of the first elementextends outside the bone; (c) providing an elongated tension elementhaving an anchor portion at a distal end thereof; (d) mating a proximalend of the tension element with the distal end of the first element; (e)pushing the tension element into the bone while maintaining the proximalend and the distal end in mating contact until the anchor portion of thetension element contacts the bone; (f) removing the first element fromthe tension element when the proximal end of the second element exitsthe bone; (g) extending the proximal end of the tension element throughone of the openings in the bone plate; (h) tensioning the tensionelement; and (i) while maintaining the tension element in tension,anchoring the tension element to the bone plate.
 12. The method forfixation of a bone fracture of claim 11, wherein the first elongatedelement is a K-wire having a sharpened tip.
 13. The method for fixationof a bone fracture of claim 11, wherein the first elongated element isdriven through the bone by a drill.
 14. The method for fixation of abone fracture of claim 11, wherein the bone plate is positioned on thebone prior to extending the first elongated element through the one ofthe openings in the plate.
 15. The method for fixation of a bonefracture of claim 11, wherein the step of anchoring the tension elementto the bone plate includes: extending a cannulated drill over theproximal end of the tension element; forming a bore at least partiallyinto the bone using the cannulated drill; extending a cannulated anchorelement along the proximal end of the tension element and through theone opening in the bone plate and into the bore formed in the bone. 16.The method for fixation of a bone fracture of claim 11, wherein thesteps (b) through (i) are repeated for additional tension elements. 17.The method for fixation of a bone fracture of claim 16, wherein the stepof anchoring all the tension elements to the bone plate includeadjusting the tension in selected ones of the tension elements prior toanchoring the selected tension elements.
 18. The method for fixation ofa bone fracture of claim 16, further comprising removing excess portionsof all of the tension elements once the tension elements have beenanchored to the bone plate.
 19. The method for fixation of a bonefracture of claim 11, wherein the step of anchoring the tension elementto the bone plate includes pushing a Tinnerman washer onto the proximalend of the tension element and into contact with the bone plate.
 20. Themethod for fixation of a bone fracture of claim 11, wherein the step ofanchoring the tension element to the bone plate includes mating apolyaxial anchor between the tension element and the bone plate, andwherein the polyaxial anchor includes a shank extendable into the bone.